the perfect typhoon

According to meteorologists, typhoons never occur near the equator. Why? Because the Coriolis effect, which gives spin to the wind due to the rotation of the Earth, is weakest there. That spin helps form the violent, swirling, circular wind-driven thunderstorms called hurricanes, typhoons, or tropical cyclones, depending on what part of the world you’re from. But in December 2001, Typhoon Vamei formed just 100 miles away from the equator, the closest ever recorded. A recent study of the storm published by meteorologists from the Naval Postgraduate School in Monterey, Calif., has helped clear up the mystery. The researchers conclude that Vamei formed due to a rare combination of a strong, warm, slow-moving storm system colliding with an equally strong surge of cold monsoon winds from the north. The unusually long-lasting interaction of the two powerful systems over the warm South China Sea generated the turning that created the typhoon. According to the study’s authors, “the probability of a similar equatorial development is estimated to be once every 100 to 400 years.”

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 4/22/2003.